I know this is not strictly a job for radius, but can FreeRadius dynamically assign ip addresses from mysql. This is a feature I have used previously in radiator and found it very useful.
I have seen the Framed-IP-Address with a + (e.g. 192.168.1.1+), but I could not find any documentation. Thanks, Ken - List info/subscribe/unsubscribe? See http://www.freeradius.org/list/users.html
